I do the exactly the same. It's a similar principle to kanban/agile, where you have a pool of potential work to do (in your case your ideas list), but you only pull in a fixed amount to work on at any one time (in your case to your TODO list). Otherwise I find I tend to get overwhelmed by my evergrowing todo list and never get anything done. Of course it's key to periodically review the ideas list, but this can just be done whenever your todo list is empty.